According to the development of multimedia and network technologies, a user is able to use a desired service through various devices and service providing servers. In addition, the user may communicate with another user by using their respective devices. The behavior patterns of the user become complex as the user uses the various devices and the service providing servers, but it is difficult for the user to effectively determine his/her obligations since the obligations are related to the various devices, other user, and service providing server. Accordingly, a technology of effectively generating a to-do list of a user by analyzing the behavior of the user and efficiently determining and notifying the user of an unperformed task from among tasks in the to-do list is required.
The above information is presented as background information only to assist with an understanding of the present disclosure. No determination has been made, and no assertion is made, as to whether any of the above might be applicable as prior art with regard to the present disclosure.